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Message-Id: <20200116164300.6705-191-sashal@kernel.org>
Date: Thu, 16 Jan 2020 11:42:46 -0500
From: Sasha Levin <sashal@...nel.org>
To: linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc: Jesper Dangaard Brouer <brouer@...hat.com>,
Alexei Starovoitov <ast@...nel.org>,
Toke Høiland-Jørgensen <toke@...hat.com>,
Andrii Nakryiko <andriin@...com>,
Sasha Levin <sashal@...nel.org>, netdev@...r.kernel.org,
bpf@...r.kernel.org, clang-built-linux@...glegroups.com
Subject: [PATCH AUTOSEL 5.4 191/205] samples/bpf: Fix broken xdp_rxq_info due to map order assumptions
From: Jesper Dangaard Brouer <brouer@...hat.com>
[ Upstream commit edbca120a8cdfa5a5793707e33497aa5185875ca ]
In the days of using bpf_load.c the order in which the 'maps' sections
were defines in BPF side (*_kern.c) file, were used by userspace side
to identify the map via using the map order as an index. In effect the
order-index is created based on the order the maps sections are stored
in the ELF-object file, by the LLVM compiler.
This have also carried over in libbpf via API bpf_map__next(NULL, obj)
to extract maps in the order libbpf parsed the ELF-object file.
When BTF based maps were introduced a new section type ".maps" were
created. I found that the LLVM compiler doesn't create the ".maps"
sections in the order they are defined in the C-file. The order in the
ELF file is based on the order the map pointer is referenced in the code.
This combination of changes lead to xdp_rxq_info mixing up the map
file-descriptors in userspace, resulting in very broken behaviour, but
without warning the user.
This patch fix issue by instead using bpf_object__find_map_by_name()
to find maps via their names. (Note, this is the ELF name, which can
be longer than the name the kernel retains).
Fixes: be5bca44aa6b ("samples: bpf: convert some XDP samples from bpf_load to libbpf")
Fixes: 451d1dc886b5 ("samples: bpf: update map definition to new syntax BTF-defined map")
Signed-off-by: Jesper Dangaard Brouer <brouer@...hat.com>
Signed-off-by: Alexei Starovoitov <ast@...nel.org>
Acked-by: Toke Høiland-Jørgensen <toke@...hat.com>
Acked-by: Andrii Nakryiko <andriin@...com>
Link: https://lore.kernel.org/bpf/157529025128.29832.5953245340679936909.stgit@firesoul
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
samples/bpf/xdp_rxq_info_user.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/samples/bpf/xdp_rxq_info_user.c b/samples/bpf/xdp_rxq_info_user.c
index c7e4e45d824a..b88df17853b8 100644
--- a/samples/bpf/xdp_rxq_info_user.c
+++ b/samples/bpf/xdp_rxq_info_user.c
@@ -489,9 +489,9 @@ int main(int argc, char **argv)
if (bpf_prog_load_xattr(&prog_load_attr, &obj, &prog_fd))
return EXIT_FAIL;
- map = bpf_map__next(NULL, obj);
- stats_global_map = bpf_map__next(map, obj);
- rx_queue_index_map = bpf_map__next(stats_global_map, obj);
+ map = bpf_object__find_map_by_name(obj, "config_map");
+ stats_global_map = bpf_object__find_map_by_name(obj, "stats_global_map");
+ rx_queue_index_map = bpf_object__find_map_by_name(obj, "rx_queue_index_map");
if (!map || !stats_global_map || !rx_queue_index_map) {
printf("finding a map in obj file failed\n");
return EXIT_FAIL;
--
2.20.1
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